Electrolytic process for producing dihydroxycapronitrile



United States Patent 3,325,381 ELECTROLYTIC PROCESS FOR PRODUCINGDIHYDROXYCAPRONITRILE Robert W. Foreman, Chagrin Falls, Ohio, assignorto The Standard Oil Company, Cleveland, Ohio, a c0rporation of Ohio NoDrawing. Filed Feb. 3, 1964, Ser. No. 342,264 12 Claims. (Cl. 204-77)The present invention relates to a process for the production ofdihydroxycapronitrile by the hydrolysis of dihydrocyanopyran toglutaraldehyde monocyanhydrin and the reduction of glutaraldehydemonocyanhydrin to dihydroxycapronitrile.

In the present invention 3,4-dihydro-2-cyano-2H-pyran or sometimesreferred to herein simply as dihydrocyanopyran, which can be preparedfrom acrolein and acrylonitrile as described in my copending US. patentapplication, Ser. No. 251,056, filed Jan. 14, 1963, now Patent No.3,153,052, is hydrolyzed in an aqueous solution of an acid salt to themonocyanhydrin of glutaraldehyde which is then reduced to2,S-dihydroxycapronitrile in an electrochemical reaction by thefollowing steps:

Step I The hydrolysis reaction may be carried out in a dilute aqueoussolution of an acid, an acid salt or in the presence of a cationexchange material. The acid, acid salt or cation exchange material is acatalyst and is not consumed in the reaction. Preferably a diluteaqueous solution of an acid sulfate is utilized which later also mayserve as the electrolyte in the electrolytic reduction step of theprocess. Such an electrolyte can be recycled after removal of thedihydroxycapronitrile, thereby simplifying the process and reducing theconsumption of acidic catalyst.

The electrolytic reduction of the glutaraldehyde monocyanhydrin may beconveniently carried out in an undivided cell, using preferably, a leadcathode and a lead dioxide or platinum anode. If a divider is used toseparate the cathode and anode compartments, a permselective cationexchange membrane is preferred. The monocyanhydrin of glutaraldehyde isfed to the cathode compartment and the product, dihydroxycapronitrile,may be recovered from the aqueous catholyte by means of solventextraction. The electrolyte can then be recycled to the hydrolysisreaction or to the electrolytic cells as desired. Selective catalytichydrogenation of the aldehyde group of the monocyanhydrin ofglutaraldehyde is difficult. With Raney nickel, for instance, hightemperatures and pressures are required to catalyze the hydrogenation,and then the nitrile group is hydrogenated in preference to the aldehydegroup. Unexpectedly, the most successful means for the conversion is byelectrolytic reduction.

The hydrolysis Step I and the electrochemical reduction Step II may beconducted in separate or the same reaction vessels in a sequential orsimultaneous manner and still be within the scope of the presentinvention. If the two steps are carried out simultaneously, however,reaction conditions must be adjusted to maximize the yields in bothreactions.

As shown by equation earlier, the product of the hydrolyzeddihydrocyanopyran (Step 1) exists as an equilibrium mixture of thealdehyde, monocyanhydrin, and the cyclic hydroxy compound,2-cyano-6hydroxytetra 'hydropyran. It is believed that the aldehyde formis selectively reduced in Step II thus shifting the equilibrium awayfrom the cyclic hydroxy compound.

In the hydrolysis Step I any water soluble acidic material having anacid strength equal to or greater than that of acetic acid (K=l.75 l0'is suitable as a catalyst. Acidic catalysts useful in the reaction ofthis invention include, but are not limited to, sulfuric acid,hydrochloric acid, other halogen acids, phosphoric acid; acid salts suchas ammonium bisulfate, sodium bisulfate, sodium acid phosphate, and thelike. Cation exchange resins in their acid forms such as sulfonatedstyrene-divinyl benzene copolymers may also be used and such materialsinclude Amberlyst-IS, Dowex-SO, Amberlyte-400, IR-20 and the like.Ammonium bisulfate is the preferred hydrolysis catalyst in the instantinvention.

The rate of hydrolysis of dihydrocyanopyran to glutaraldehydemonocyanhydrin depends upon temperature and degree of acidity. Thehigher the temperature and the greater the acidity, the shorter thetimerequired for reaction to a given conversionfFor instance, at C. aminimum of 0.05 N strong mineral acid, such as sulfuric, is required inorder to achieve hydrolysis in a reasonable length of time, whereas atroom temperature an acidity of 2.0 N strong acid is necessary forpractical hydrolysis rates. With 5 or 6 N strong acid, hydrolysis iscompleted in a matter of a few minutes. The preferred reactiontemperatures range from about room temperature to C. or slightly higher.Preferably dihydrocyanopyran is fed to the hydrolysis reaction mixturein proportions such that the resulting monocyanhydrin ofglutaraldehydeis soluble in the reaction medium and for an aqueous acidmedium this isgenerally about 3040% by Weight. I

Although either a divided or an undivided cell may be used in theelectrolytic reduction step, there is some preference for the use of adivided cell because some dihy' droxycaproic acid forms in the undividedcell by anodic hydrolysis of the nitrile group. The dihydroxycaproicacid will probably impede dihydroxycapronitrile formation andcrystallization. It is estimated that approximately onethird of thedihydroxycapronitrile produced by electrolysis in an undivided cell ishydrolyzed to the hydroxy acid.

It the membrane is used to separate the reactions at the anode and thecathode, it is preferred that a cationic permselective ion exchangeresin be utilized. Any commercially available permselective cationicmembrane such as Permutit 3142 or AMF-ion C102 would be suitable.

The preferred cathode composition is lead. Actually, the cathodematerial maybe any conductive material that is passive under theinfluence of the cathode voltage as for example, cadmium, mercury,steel, iron, nickel and the like. Material selected for the anode mustbe resistant to the action of strong acids under anodic oxygen.Preferably the anode is composed of lead dioxide or platinum.

For a more simplified and economical operation, the same acid mediumthat is employed in the hydrolysis may also be employed as theelectrolyte. Again ammonium bisulfate is preferred. The concentration ofthe acid in the electrolyte solution is controlled by three factors.Sutficient acid must be present to provide conductivity and to aidsolubilization of the monocyanhydrin of glutaraldehyde in theelectrolyte at practical levels, e.g., in amounts of about 1 to 3 moles.The loss of excess acid in the separation of dihydroxycapronitrile fromthe reaction medium should be minimized. If dihydroxycapronitrile isrecovered by means of an immiscible solvent, the use of excess acid willtend to solubilize the solvent. It is therefore preferred that theacidity of the electrolyte be in the range equivalent to from about .05moles of sulfuric acid per liter or a normality of 0.1 up to 10 moles ofsulfuric acid per liter or a normality of 20.

The electrolytic reduction is usually carried out at temperaturesranging fi'om about room temperature to about 45 C. However,temperatures of from 20 C. to 60 C. are operable.

The current densities in the electrolytic cell may vary widely.Generally the current density should fall within a range of 5 to 100amps per square foot and a range of 20 to 50 amps per square foot ispreferred. Theoretically, at least two Faradays of electricity arerequired to reduce one mole of the monocyanhydrin of glutaraldehyde toone mole of dihydroxycapronitrile.

The dihydroxycapronitrile produced by the present process is a knowncompound which is useful in some cases as a solvent and also as anintermediate glycol material in the preparation of alkyd resins bycondensation with a dibasic organic acid or its anhydride.

The present invention is further illustrated in the following exampleswherein the amounts of ingredients are expressed as parts by weightunless otherwise indicated.

EXAMPLE I Step I reactions employing various acids and acid salts atvarying concentrations and reaction conditions are illustrated in detailin Table I. In each case the conversion of dihydrocyanopyran to theequilibrium mixture of the monocyanhydrin of glutaraldehyde and thetetrahydrohydroxycyanopyran was complete.

The hydrolysis of dihydrocyanopyran was conducted either in amechanically stirred flask or the agitation was supplied by shaking thereaction flask. Water bath heating was used until the visibledissolution of dihydrocyanopyran occurred and then the hydrolysiscontinued for about to 30 minutes thereafter. When Amberlyst resin wasused, it was converted to the acid form and then washed with water priorto use in the hydrolysis reaction. v20 grams of resin per 100 ml. ofwater and 0.1 mole of dihydrocyanopyran were used. Trc monocyanhydrin ofglutaraldehyde was isolated by neutralizing the hydrolyzed product withsodium carbonate containing some sodium sulfate or sodium chloridefollowed by extraction with ether. The ether was then removed carefullyfrom the hydrolysis product at near room temperature and under nitrogen.

The analytical determination of the monocyanhydrin of glutaraldehyde wascarried out by adding excess hydroxylamine hydrochloride solution to anappropriately sized sample. Reaction of the aldehyde with hydroxylaminecaused the liberation of hydrogen chloride which was determined bytitration with standard base. The Amberlyst 15 resin appearing in TableI is a sulfonated copolymer of styrene and divinyl benzene.

EXAMPLE II The electrolytic reduction Step II is illustrated in thisexample. Two different electrolysis cells were used in conducting theexperiments. One cell consisted of two, threeinch diameter cylindricalplastic sections 1 /2" thick and /s" thick sandwiched together with discelectrodes at each end. A semipermeable sulfonated styrene-divinylbenzene copolymer membrane supported on a polyester web (Permutit 3142)was sandwiched between using rubber gaskets for sealing. The entireassembly was held together in an insulated wood vise. A mechanicallydriven angular glass rod provided stirring in the larger compartmentwhich served as the cathode chamber. Electrical connections were made byclips to ears on the electrodes. A sixvolt adjustable DC. power supplyand suitable volt meter and am-meter Were also in the circuit.

The second cell was designed so that many cells could be stackedtogether in a minimum space. Flow-through provided stirring, and cellcircuitry was the same as for the cell described above. In operatingeither cell, the electrolyte was charged to both chamberssimultaneously. The monocyanhydrin of glutaraldehyde was added eithergradually to the catholyte or was present initially. Experiments wereconducted and remained at current and voltages where little or nocathode gas ing took place. The experiments were continued to apredetermined Faraday/ monocyanhydrin of glutaraldehyde ratio. In thesecond cell, circulation to and from the reservoir occurred at such arate that the cell residence time was approximately 30 seconds. Thecirculation was on the order of 300 cc. per minute.

TABLE I. HYDROLYSIS CONDITIONS Hydrolysis Medium Temp., Time, G. DHCP,Mixing Procedure Post Treatment Recovery 0. Hours 100 cc. (Percent) 20.1 N H01 3.0 25 Ozree stirred flask Neut. to pH=2, add NaCl,

ether extracted. 0.1NHO1 80 2.0 25 do 92 0.1 N H01- 90 1.0 10 Neut. topH=4, not salted, -72

ether extracted. 0.5 N HCl 1.67 15- 6 1O Hydrogenated aqueous solutionas produced. 0,02 N H 3. 5 10 d0 Neut. to pH=2, add NaCl, 75

ether extracted. 120 1. 0 10 Heated in earius tube-not Salted w. NaOl,either exshaken. tracted. 0.05 N HzSO; 90 2.0 10. 9 Stirred flask. Neut.w. OaCOa filtered, 89

ether extracted. 0.1 N H SO; 90 .75 Neut. to pH=3, Na SO4 added, 75

. ether extracted. 0.5 N 112804 90 1.0 Neut. to pI-I=4 1.0 M NaHSOr 900. 5 o None H O+5 w./w. Percent 25 48 Mechanical shak Ether extracted.76

Amberlyst-l5 Acid Ion Exchange Resin. 7 HzO-l-fi w./w. Percent 0.20 10.9 Stirred flask under reflux Deeply ether extracted 88 Amber1yst-15 AcidIon Exchange Resin.

1 Dihydrocyanopyran.

= Not determined.

Experimental examples showing the feasibility of a number of differentelectrodes, electrolytes, and reaction conditions are summarized inTable II. The analysis of unreacted monocyanhydrin of glutaraldehyde anddihydroxycapr-onitrile was made as the electrolysis proceeded. Theanalytical procedure for the determination of dihydroxycapronitrileincluded adding an excess of 0.1 normal silver nitrate to a suitablesize sample, adjusting the pH with caustic to 7.5 until the pH remainedat that level for a minimum of five minutes. The silver cyanide producedwas removed by filtration, the pH was adjusted to the acid side withdilute nitric acid, and the excess silver ion was determined bytitration with standard potassium thiocyanate to a ferric alum endpoint. If too much sulfate was present in the sample, it was removed asbarium sulfate before proceeding with the analysis.

In Table II the Faraday-to-mole monocyanhydrin of glutaraldehyde ratiowas slightly greater than 2. The conversions varied from about 69 to100%.

4. The process of claim 3 wherein the hydrolysis is carried out at atemperature in the range of from about room temperature to slightlyabove 100 C.

5. The process of claim 4 wherein the electrolytic reduction is carriedout at a temperature in the range of from about to C.

6. The process of claim 5 wherein the electrolytic reduction is carriedout at a current density of from 5 to 100 amps. per square foot.

7. The process of claim 6 wherein the acid catalyst is present in aconcentration of from 0.5 N to 20 N.

8. The process of claim 7 wherein the acid catalyst is a member selectedfrom the group consisting of sulfuric acid, hydrochloric acid, otherhalogen acids, phosphoric acid, sodium bisulfate, ammonium bisulfate,sodium acid phosphate, and cation exchange resins in the acid form.

9. The process of claim 8 wherein the acid catalyst is hydrochloricacid.

TABLE II Feed Final Electrolyte Cell 2 IMOHG, 100 cc. MCHG 1 SourceAddition Method Electrolyte Catholyte plus Cone. Anolyte plus Cone.Cathode Temp. C.

l Molar NaI-ISOi hydrolyzate All in at start 11. 4 1.0 M NaHSO 1 MNaHSOi I-Ig, Pb

(94% yield from DHCP Amberlyst hydrolyzed do 10. 6 207 cc. 1.0 N H cc.1.0 N I'I2SOJ Cd 32-40 DHOP -86.4% yield (.1

mole/100 cc./20 g. resin). Concd (in vacuo) aq. soln Added gradually 7.82 cc. 1.0 M NaT-ISO; at cc. 1.0 M NaHSO4 Fe (Steel) 30-40 fromAmberlyst hydrolystart. Final calcd v0l.=

mate-84% yield. Yield 0 cc.

85% but not accurately determined. Concd aq. Amberlyst .d0 10. 0 140 cc.1.0 M NH4HSO4 at 140 cc. 1.0 M Cd 27-38 hydrolyzate (82% yield) start.Final calcd vol.= N HlHSOi.

cone. to 2.6 M in aldehyde. 200 cc. 1 M NH HSO4 hydrol. Continuous cir-10.8 1,500 mi. 1 M NH HSO 120 ml. 1 M Pb, not pre- Ambient.

DHOP 2 (92% yield). culation with MGHG'.1 NH4HSO4. eondit.

withdrawals plus addns.

1 Monocyanhydrin of Glutaraldehydc. 2 Dihydrocyanopyran.

I claim:

1. The process for the manufacture of 2,5-dihydroxycapronitrilecomprising hydrolyzing 3,4-dihydro-2-cyanor ZH-pyran in an aqueousmedium in the presence of an acid catalyst to form the rnonocyanhydrinof glutaraldehyde and electrolytically reducing the monocyanhydrin ofglutaraldehyde in an aqueous medium in the presence of an electrolyte to2,S-dihydroxycapronitrile.

2. The process of claim 1 wherein the acid catalyst is a material whichhas an acidity of at least K=1.75 10- No references cited.

JOHN H. MACK, Primary Examiner.

3. The process of claim 2 wherein the electrolyte i D. R. VALENTINE,Assistant Examiner.

the same as the acid catalyst.

1. THE PROCESS FOR THE MANUFACTURE OF 2,5-DIHYDROXYCAPRONITRILECOMPRISING HYDROLYZING 3,4-DIHYDRO-2-CYANO2H-PYRAN IN AN AQUEOUS MEDIUMIN THE PRESENCE OF AN ACID CATALYST TO FORM THE MONOCYANHYDRIN OFGLUTARALDEHYDE AND ELECTROLYTICALLY REDUCING THE MONOCYANHYDRIN OFGLUTARALDEHYDE IN AN AQUEOUS MEDIUM IN THE PRESENCE OF AN ELECTROLYTE TO2,5-DIHYDROXYCAPRONITRILE.